Electric standard seamless hot-pressing elbow is mainly used in boiler pipe in the pipe system such as, thermal power plant, with the increasing of electric installation unit capacity, such as main steam steaming-water pipe design is becoming more and more thick, and many have reached more than 70 mm thick, traditional pipe welding operation cannot meet the needs of factory piping, therefore, must improve the thick-walled elbow welding process. Take thick wall elbow of P91 steel as an example, preheat before welding and track the temperature between layers. According to the analysis of P91 welding performance, the preheating temperature and weld layer temperature must be strictly controlled. The preheating temperature of TIG welding is 100 ~ 150℃, and SMAW heating up to 250 ~ 300℃. In the whole welding process, far-infrared thermometer is used to monitor the temperature between weld layers. Argon - filled protection is used in welding. Due to the high alloy content of P91 steel, the liquid iron is poor and the root is easy to be scorched. Argon can fully protect the metal molten pool from oxidation and improve the mechanical properties of welding seams. Before welding, a simple argon filled device was made according to the actual situation to form an gas chamber inside the pipeline, which can ensure the welding joint quality of the thick-wall elbow. P91 molten iron fluidity is poor, so the weld of thick wall elbow is easy to form slag inclusion. Angle grinder is used to clean on site, but not hammer or chisel to avoid cracking. In addition, according to the requirements of welding Procedure, welding joints with wall thickness greater than 70m must be inspected between layers. When the weld thickness reaches 20 ~ 25mm, stop welding, immediately carry out heat preservation and other post-heat treatment, and continue welding after passing RT inspection.